The systems and methods of the invention relate to the suppression of acoustic pressure waves, and in particular, to the suppression of acoustic pressure waves in gas turbine combustion chambers.
It should be appreciated that adverse acoustic pressure waves may be generated in a variety of operational systems. For example, such adverse acoustic pressure wave may be generated in gas turbines. This problem may manifest itself when trying to increase the efficiency of the flames in the combustion chambers of such a gas turbine, for example. That is, the problem may manifest itself when trying to reduce the undesirable emissions generated by a gas turbine. By reducing the emissions, and the rate at which governmental emissions allotments are consumed, it is possible to maximize the number of revenue hours of the gas turbine.
That is, when the flames are “leaned out,” the emissions go down. However, the flame burning in the gas turbine may become unstable. Such an unstable flame creates a pressure wave, which may be of audible frequencies, and hence termed an “acoustic pressure wave.” The acoustic pressure waves may stress various portions of the gas turbine, causing fatigue and shortening the life of the turbine. Specifically, torsional vibrations on the gas turbine's shaft may be created resulting in flexing and stressing the turbine blades. Additionally, the acoustic pressure wave may damage internal baffling in the combustion chamber. The acoustic pressure wave may also adversely affect the efficiency of the machine.
There are known techniques relating to the active suppression of combustion chamber acoustics. However, the known techniques fail to teach an effective process to establish a corrective modulation signal at the correct magnitude, frequency and phase. Some known techniques create a modulation signal using adaptive filtering. The difficulty with such a technique lies in the need to, and time required for, filter coefficients to adapt when the acoustic signature is changing spectral content rapidly. Also, in the absence of any automatic gain control, the known techniques may actually exacerbate the undesired acoustic while re-adapting to the new spectral content. Accordingly, the known techniques suffer from the above drawbacks, as well as others.